The present invention is directed to the fields of energy consumption management systems, electrical demand charge control, and related fields.
Electricity consumers in recent years have been faced with rising energy costs and rising needs to address environmental and efficiency concerns in the grid. Energy consumption management systems have been developed with these needs in mind to reduce energy consumption during periods having higher electricity costs, to expand the availability of charging electrically-powered vehicles, to participate in demand response programs hosted by utilities, and to counteract the appearance of demand charges assessed by utilities, among other goals. To prevent or diminish the appearance of demand charges, typical consumption management systems employ curtailment techniques such as load shedding, prioritization, and cycling to reduce demand during peak periods when demand charges would otherwise be registered by utility meters. Some management systems include energy storage devices such as battery banks that are discharged at these peak times in such a manner that the net load on the grid is mitigated even if the usage of the loads at the site goes unchanged.
When using energy storage devices or generators to supply energy to a site for consumption management, a system controller monitors the overall consumption of the site and discharges the energy storage or starts up a generator when the consumption is too high. This gives rise to a number of problems. One is the delay between detecting excess consumption and providing energy to the site for sites where an inverter is controlled in response to a command signal. The controller must register that the consumption has surpassed a limiting value, then the controller must send instructions to the energy storage or generator, and then the energy storage or generator must provide the energy required. It is common for a spike in demand to have already subsided before the energy provision takes place, and even if the peak has not subsided, the utility meter has already recorded at least a portion of the peak that exceeds the limiting value. These issues may not be present when an inverter is used that converts power on demand, but the load may still fluctuate dramatically enough that circuit breakers or protective relays are tripped, and the load profile of a mitigated load is usually still erratic.
The reactive design of these systems leaves uncertainty regarding how much consumption will actually be recorded by the utility. Higher sampling rates tend to reduce the uncertainty and allow the system to more closely follow an idea “flat-line” of consumption, but even at high sampling rates there is a chance that protection relays may be triggered before action can be taken. Furthermore, sudden loss or gain of load creates a risk of back-feeding energy to the grid or tripping protective breakers that do not automatically reset. Back-feeding is dangerous to local utility providers as it adds to the risk of tripping network protectors. Additionally, the sampling rate and extreme twitch capability of these systems drives up their complexity and cost, and can damage or at least excessively cause wear to energy storage devices, generators, switches, and other components.